We plan to test the hypothesis that mechanoreceptors in the lung or chest wall help to determine the level of alveolar ventilation in chronic obstructive lung disease. Since study of the effect of chronic obstructive lung disease on respiratory mechanoreceptors and their role in the control of breathing is difficult in man, the physiologic features of chronic obstructive lung disease will be produced in dogs by the administration of papain. The lung and chest wall mechanoreceptors will be assessed in conscious and anesthetized animals before and serially during the course of lung disease. The effects of stimulation or block of mechanoreceptor afferent activity on respiratory neural activity will be assessed from diaphragmatic electrical activity, occlusion pressure, and ventilation. The contribution of vagal mechanoreceptors to resting and chemically stimulated breathing will be assessed from the effects of vagal cooling. The sensitivity of vagal stretch and irritant receptors will be tested indirectly in conscious animals from the response to changes in tidal volume and aerosolized histamine, respectively and directly in anesthetized animals from single fiber recording. To determine whether changes in central processing of vagal mechanoreceptor afferent activity occurs in papain emphysema, electrical activity of the whole nerve will be recorded in both anesthetized and conscious animals and related to respiratory motor activity. The contribution of chest wall mechanoreceptors to respiratory adjustments during resting and chemically stimulated breathing will be assessed from the level and pattern of respiratory activity during vagal blockade. Chest wall mechanoreceptor function will be evaluated from the change in respiratory activity produced during vagal blockade by external ventilatory loading and intercostal muscle vibration. Mechanoreceptor afferent activity will be correlated with non-invasive tests of receptor sensitivity and indices of lung structure and function to help find mechanoreceptor tests which are applicable to man.